The objective of this article is to review the in vivo and in vitro effects of using levonorgestrel (LNG) as emergency contraception (EC) on sperm function. Seven articles and an abstract containing data on the effects of using LNG as EC on sperm function were reviewed. Except for two early studies, in vitro and in vivo studies showed no significant effect of using LNG as EC on the number of spermatozoa penetrating the cervical mucus and reaching the uterine cavity, the number of spermatozoa adhering to the Fallopian isthmus or ampulla, or the number of spermatozoa adhering to the human tubal epithelium. Furthermore, no effect was found on sperm–zona pellucida binding capacity or the percentage of spermatozoa with D-mannose receptors when testing physiological doses of LNG. The only significant effect was a dose-dependent impairment of sperm motility. In conclusion, as EC, LNG does not apparently affect sperm function in vitro or in vivo. However, further studies should be conducted in order to evaluate the adhesion of spermatozoa to the tubal epithelium and the capacitation process, or a mechanism in which LNG disrupts the process of spermatozoa binding to the Fallopian endosalpinx and interferes with the process of fertilization, in order to clarify the mechanism of action of LNG as EC.